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Full text of "Text Book Of Mechanical Engineering"

6                               Simple Moulding.



f

A Cattle Trough.—Our next example of moi
ordinary cattle trough, and here two boxes are used
sand. The pattern may be of wood in the first inst;
the same shape as the finished casting. It is pi
bottom box, as in Figs. 5 and 6, and sand is filled in to
which is the parting. This parting is smoothed off, :
parting sand applied, and, the top box being put on 2
down, the whole is filled with sand and rammed w<
The top box must now be removed and the pattern
a slight rapping being given to effect its detachme
/ "sand, while the latter is dusted with Blackening, w
charcoal dust. But first, to make the blackening ad
meal is sprinkled on the mould, absorbing the damp
and thus becoming a pasty layer. The object of th*
is this: If the metal were to touch the side of the mo
enter into the sand surface, and thus produce a roi
This is allowable in moulding boxes, where roughness
advantage, but where a smooth casting is desired, b'
needed, as it ignites on being touched by the metal, a
a film of gas between it and the mould, a clean castir
result. (See pp. ^747 and 1012.)

Gates.—The mould having been sleeked and f
any little break in the sand mended, the gates havi
made for the entrance of the metal. Tapering plugs
usually left in the sand for that purpose, and these are n<

The more shallow the casting, the more gates a
many even as four.

Vent Holes are made in the more solid parts
(but not to touch the surface of the mould) to fi
passage of air from the latter.

The moulders, being provided with molten iron,